Algorithms/Results (SO 2 and ash) based on SCIAMACHY and GOME-2 measurements

Transcription

1 ESA/EUMETSAT Workshop on Volcanic Ash Monitoring ESA/ESRIN, Frascati, May 2010 Algorithms/Results (SO 2 and ash) based on SCIAMACHY and GOME-2 measurements Nicolas THEYS H. Brenot, J. van Gent and M. Van Roozendael (BIRA-IASB) P. Valks, M. Rix, D. Loyola (DLR) R. Van der A (KNMI) A. Richter (IUP Bremen)

2 - Contents - Support to Aviation Control Service (SACS) Example of results for the eruption of the Eyjafjallajokull volcano Algorithmic developments European Volcano Observatory Space Services Ash plume from the Eyjafjallajokull eruption on 15 Apr Saeberg/Reuters

3 Support to Aviation Control Service (SACS) developed for ESA, within DUE (TEMIS) and GSE (PROMOTE) programmes started in 2006, now extended for 3 years (SACS+) The Support to Aviation Control Service (SACS) intends to deliver in nearreal time data from space-based instruments regarding SO 2 and aerosol (ash) data possibly related to volcanic activity. In case of an event notifications are send by to users pointing them to a dedicated webpage with detailed information. If possible information on the location, elevation and motion of volcanic plumes will also be provided in collaboration with the SAVAA project. Volcanic Ash Advisory Centres (VAACs) Notifications of events and data from SACS+ can be useful to the VAACs and other interested users: volcanic observatories, air quality monitoring institutes, scientist, etc. Currently: 66 subscribers

4 Volcanic SO 2 services DLR: GOME-2 IUP Bremen: GOME-2 ULB: IASI SAVAA GOME-2 SO2 alert service:

5 Partners in SACS Belgian Institute for Space Aeronomy (BIRA-IASB) leader N. Theys, H. Brenot, J. van Gent and M. Van Roozendael Royal Netherlands Meteorological Institute (KNMI) R. van der A and Roeland van Oss Free University of Brussels (ULB) P. Coheur, L. Clarisse and C. Clerbaux German Aerospace Center (DLR): data provider P. Valks, M. Rix, D. Loyola

6 Data products of SACS Near-real time and archive service Instrument Data type Participants Data products Availability Alerts SCIAMACHY UV/visible BIRA SO 2 columns + + (ENVISAT) KNMI absorbing aerosol index + GOME-2 (MetOp-A) UV/visible DLR KNMI SO 2 columns* absorbing aerosol index + [+] [+] OMI UV/visible KNMI SO 2 columns + [+] (Aura) absorbing aerosol index + IASI Infrared ULB SO 2 index and columns [+] [+]** (MetOp-A) ash indicator [+] + = currently available [+] = to come during SACS+ * Operational product from DLR. ** IASI alerts currently available via ULB. [ All four sensors are nadir viewing instruments on near-polar sunsynchronous orbits]

7 SACS portal (hosted by BIRA-IASB)

8 Alert system: subscription to list

9 Alert system Eruption of the Vanuatu.. currently only based on SCIAMACHY data Criteria for exceptional SO2 events For each pixel with SO 2 SCD>3 DU, the 8 surrounding pixels are evaluated: -SO 2 SCD>3 DU: + 1 point -SO 2 SCD<0 DU: -1 point SACS notification of exceptional SO2 concentration ================================================== Process date : Process time : 23:56:01 CET Instrument : SCIAMACHY No. notices : 1 Alert notice : Start date : Start time : 22:45: UTC Aver. long. : deg. Aver. latit. : deg. Aver. sza : 24.5 deg. Max. SO2 vcd : 41.3 DU Remark : If points 5 then an alert is triggered and an is sent to interested users

10 Ongoing development: multi-sensors approach Aim: improve global alerts by using polar orbiting nadir sensors IASI SO pm am

11 Multi-sensors approach SCIAMACHY is the worst instrument for an alert system (global coverage achieved in 6 days) Using data from satellite instruments with different overpasstimes is relevant to reduce the t between the time of the eruption and the time when the alert is sent. 09:30 am GOME-2, IASI 10:00 am SCIAMACHY night day 01:30 pm OMI IASI Possibility to associate a level of confidence to an event if it is observed by several sensors. However, a high level of confidence is at the expense of a small t! The synergistic use of GOME-2 and IASI data (both on MetOp-A) enables to discriminate surface SO 2 from FT/stratospheric SO 2.

12 The eruption of the volcano Eyjafjallajokull The eruption started on 14 th of April with little SO 2 detected (maybe obscured by the ash cloud). GOME-2 SO 2 15 April 2010 After the 23 rd of April, the evolution of the eruption has lead to a much stronger signal coming from SO 2 Operational product. Image produced by DLR

13 The eruption of the volcano Eyjafjallajokull April May GOME-2 SO2 Combined SCIAMACHY and GOME-2 SO2 images Period: 23/04 17/05, 2010 SACS has generated more than 50 alerts for this period Operational product. Images produced by DLR

14 The eruption of the volcano Eyjafjallajokull GOME-2 monitoring of SO 2 plume Main area affected to the south and west Main SO 2 emissions in 2 nd phase of eruption Largest individual values and largest total mass not at the same time Overall Impact of Eyjafjallajoekull SO 2 plume

15 Absorbing Aerosol Index Absorbing aerosol index (AAI) is calculated based on the measured reflectances at 340 and 380 nm and indicates for the presence of elevated absorbing aerosols (volcanic ash but also desert dust and biomass burning). meas I I I I AI 100 log 10 0 log10 0 SCIAMACHY AAI data available on SACS website (GOME-2 available soon). SCIAMACHY and GOME-2 AAI products are produced by KNMI => more in P. Stammes s talk Ray

16 Algorithmic developments SCIAMACHY and GOME-2 SO 2 VCD retrieval starting point: DOAS approach (three steps) 1. SO 2 slant columns (integrated concentration along the mean optical light path) are retrieved from satellite measurements with a DOAS technique in the range nm. DOAS fits a calculated spectrum which is based on the cross sections of SO 2, ozone and Ring effect and on a reference spectrum against the measured spectrum.

17 Algorithmic developments 2. Background correction for the offset due to the reference spectrum and the anticorrelation between SO 2 and O 3 observed at high solar zenith angles (high latitudes), due to strong ozone interferences. 3. SO 2 vertical columns are calculated by applying an air mass factor to account for the light path enhancement w.r.t. to the vertical path. VCD=SCD/AMF AMFs look-up-tables (calculated using Lidort RTM) with a set of entries (SZA, Viewing geometry, albedo, cloud fraction and cloud top pressure) and for 3 different plumes heights (boundary layer, freetroposphere and stratospheric conditions).

18 Algorithmic developments Alternative approach: iterative volcanic SO 2 retrieval (IUP Bremen) Problem: For large volcanic eruptions, the relation between absorption signal and SO 2 column becomes non-linear Solution: Iterative procedure Results: improved retrievals Larger SO 2 columns Change in SO 2 spatial pattern => significant improvement!

19 Algorithmic developments Alternative approach: direct fitting (BIRA-IASB) Tool GODFIT is a direct fitting algorithm that includes LIDORT as forward radiative transfer model and a state-of-the-art Rotational Raman Scattering (RRS) code Inversion techniques in development - volcanic ash/aerosol retrieval based on the different light intensity and RRS response of absorbing/non absorbing aerosols (LIDORT-RRS is the baseline forward RT code in GODFIT) - improvement of the SO2 VCD retrieval (high SO2 signal) - retrieval of the peak altitude of the SO 2 plume (particularly interesting for the VAACs).

20 SO 2 plume height retrieval Preliminary results: tests on synthetic UV spectra ( nm) generated by LIDORT for a predefined standard atmosphere with the contribution from R. Spurr (RT Solutions, Inc.) SO 2 : 0.5 DU SO 2 : 1.5 DU SO 2 : 15 DU Height: 2.5 km (truth) 3.2 km (retrieved) Height: 5.5 km (truth) 5.58 km (retrieved) Height: 5.5 km (truth) 5.5 km (retrieved)